(1) Field of the invention
The present invention generally relates to a centralized supervisory system for supervising network equipments, and more particularly to a centralized supervisory system capable of effectively confirming that many network equipments are operating normally.
(2) Description of the related art
Recently, in order to effectively carry out the maintenance of many network remote equipments located at different sites, a centralized supervisory system having a central supervisory device for centrally supervising the network equipments has been greatly required, the central supervisory device being located at the nucleus of the system.
A conventional centralized supervisory system for network equipments has a hierarchical structure in which a central supervisory device located at a top thereof gathers performance data and trouble data from a plurality of network equipments communicating with each other in polling operations. The performance data indicates the quality (e.g. a bit error rate) of lines in the network and varies in short intervals (a second order). The trouble data indicates troubles, such as occurrence of a line open state and a power off state, occurring in the respective network equipments and irregularly varies. The performance data and the trouble data output from the respective network equipments are successively sent from supervisory devices in a lower order-layer to supervisory devices in an upper order-layer and are finally gathered into the central supervisory device. The central supervisory device confirms, based on the performance data gathered therein, whether or not the respective network equipments operate normally, and detects troubles suddenly occurring in the network equipments, based on the trouble data.
In a small-scale system having a small number of network equipments, the central supervisory device can gather the performance data output from the respective network equipments without problems. However, in a large-scale system having a large number of network equipments, communication lines and communication processes are occupied by the transmission of a large amount of performance data, so that there is a case where this matter interferes with trouble detecting processes which must be primarily performed. In addition, in a case where supervisory results are recorded in the central supervisory device, a memory for storing the supervisory results becomes full in a short period of time. Further, there is a case where each supervisory device in each layer is provided with a buffering memory for temporarily storing received data in order to compensate for the delay of the process and to compensate for troubles of other supervisory devices. In this case, the buffering memory also becomes full of performance data in a short period of time.